The present invention relates to a catheter and cannula assembly particularly, although not exclusively, for use in medical practice.
Assemblies of a catheter sliding within a cannula are known for a number of applications. One of the difficulties which arises in the use thereof is that when the distal tip of the cannula has been urged into an opening, it is no longer possible to ascertain the precise depth of penetration of either the cannula or, in use, the catheter sliding within.
In vitro fertilization has been an established medical technique since 1978. An essential device used in placing embryos into the uterus of a recipient is a catheter which can be utilized to enter the cervical canal per vaginum and to deposit the embryos into the uterus without damage. Such a catheter needs to utilize a soft and flexible synthetic polymer in order to avoid trauma to the cervical canal; this of course presents problems in directing the catheter via the cervical canal.
This problem has, in part, been overcome by the utilization of a catheter having a generally rigid outer sheath which is provided so that during the initial direction of the catheter to the external os of the cervical canal, the sheath can be moved to protect the distal tip of the catheter. The catheter can therefore be carried by the cannula through the cervical canal as far as the internal cervical os whereupon the catheter can be moved into the uterine cavity. The catheter can then be advanced and the sheath retracted.